The present invention relates to an apparatus for heating a fuel to a predetermined temperature with a heat exchanger.
Hydrocarbon based fuels such as gasoline, kerosene, and diesel fuel, are more efficient if they are heated prior to combustion. The efficiency and engine performance is increased while the exhaust emissions are decreased as the temperature of the fuel is raised. In colder temperatures, the fuel has long chain hydrocarbons and waxes, such as laquers, which form molecules that become progressively larger with decreasing temperature until the fuel gels. Even if the fuel is flowing, the long chain hydrocarbons and waxes may be large resulting in limited atomization. Heating the fuel increases the vaporization of these molecules.
U.S. Pat. No. 5,443,053, issued to Johnson, discloses a fuel heater with a heat exchanger that employs an engine heated coolant fluid or an electric immersion heater as a source of heat. U.S. Pat. No. 5,218,944, issued to Leonard, discloses a fuel preheating system that also employs engine heated coolant fluid to preheat the fuel. The preheated fluid is then mixed with cooled or unheated fuel to produce the fuel temperature required for optimum performance. Canadian Patent No. 960,534, issued to Zuk, discloses winding a copper fuel line around a portion of a copper coolant fluid line conducting coolant heated by the engine to preheat gasoline. Canadian Patent No. 1,015,234, issued to Lebowitz et al., discloses the use of a heat exchanger and heated coolant fluid to raise the temperature of the fuel.
Fuel heaters which use engine coolant as a heat source and are comprised of a tube carrying fuel arranged around a chamber filled with the engine coolant are known to heat fuel to temperatures which very substantially. Accordingly, there is a need for an improved apparatus for preheating a fuel to an optimum temperature.
The invention disclosed provides an apparatus for heating a fuel, which comprises a block of heat conductive material. The heat exchanger block contains a passageway in which is located a heating element operative to heat the block. A fuel conduit in contact with the surface of the heat exchanger block conducts heat from the heat exchanger block to the fuel flowing within. The heat exchanger block is shaped in order to maximize the surface area in contact with the tubing or fuel conduit. The fuel conduit is made of copper or aluminum.
Advantageously, the apparatus includes a temperature sensor, which senses the temperature of the fuel passing through the fuel conduit and flowing out of the output of the fuel conduit. The sensor may be coupled to a controller that adjusts the current flow through the heating element when the temperature of the fuel falls above or below a predetermined upper or lower limit, respectively.
The apparatus may include a casing around the heat exchanger block and fuel conduit to minimize heat loss. The casing may contain or be formed of a heat insulating material, such as nylon.
By using only a ceramic heat exchanger block that has a heating coil within directly contacting the fuel conduit over an appreciable portion of the latter, high heat conductivity to the fuel is established with a relatively low heat capacity attributable primarily to the ceramic heat exchanger block. As a result, a fast response time to temperature change requests is achieved. Unlike prior art systems, there is no need to heat up a large amount of material within the apparatus with the large associated heat capacity of that material. As a result, response time in the present invention is maximized.